1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member having improved electrophotographic characteristics, and more specifically it relates to an electrophotographic photosensitive member having a photosensitive layer containing a compound with a specific structure.
2. Related Background Art
An organic electrophotographic photosensitive member containing an organic photoconductive compound as the main component has many advantages, and for example, it is free from drawbacks of an inorganic photosensitive member regarding film-forming properties, plasticity and manufacturing cost. Therefore, in recent years, much attention has been paid to the organic electrophotographic photosensitive member, and many techniques concerning the same have been suggested and some of them have been put into practice.
As such an organic photosensitive member, there has been suggested an electrophotographic photosensitive member mainly comprising a photoconductive polymer typified by poly(N-vinylcarbazole) or a charge transfer complex made from a Lewis acid such as 2,4,7-trinitro-9-fluorenone.
This kind of organic photoconductive polymer is better in lightweight properties and film-forming properties as compared with an inorganic photoconductive polymer, but the former is inferior to the latter in sensitivity, durability and stability to environmental change. For this reason, the organic photoconductive polymer is not always satisfactory.
Later, the electrophotographic photosensitive member of a separate-function type, which comprises different substances each bearing a charge-generating function or a charge-transporting function, has brought about improvements in sensitivity and durability which has made conventional organic photosensitive members disadvantageous. Such a separate-function type of photosensitive member is advantageous because the substances for the charge-generating substance and the charge-transporting substance can be selected respectively from a wide range of substances, which allows easier production of the electrophotographic photosensitive member having desired properties.
As the charge-generating substance, there have been known azo pigments, polycyclic quinone pigments, cyanine dyes, squaric acid dyes and pyrylium salt dyes. Above all, the azo pigments are preferable because of strong light resistance, high charge-generating ability and the relatively easy synthesis of materials and the like, and many kinds thereof have been suggested and put into practice.
Examples of the known charge-transporting substances include pyrazolines in Japanese Patent Publication No. 52-4188, hydrazones in Japanese Patent Publication No. 55-42380 and Japanese Patent Application Laid-open No. 55-52063, triphenylamines in Japanese Patent Publication No. 58-32372 and Japanese Patent Application Laid-open No. 61-132955, and stilbenes in Japanese Patent Application Laid-open Nos. 54-151955 and 58-198043.
The charge-transporting substance can be classified into a hole-transporting type and an electron-transporting type, but the above-mentioned charge-transporting substances and most of charge-transporting substances used in the organic electrophotographic photosensitive members which have been put into practice so far are of the hole-transporting type. In many cases of the photosensitive members each comprising the charge-transporting substance with hole-transporting ability, each photosensitive member has a conductive support, a charge-generating layer and a charge-transporting layer in this order, and in this case, the polarity of the charge which moves to the photosensitive member is negative. When the polarity of the charge is negative, ozone is generated at the time of charging and causes the photosensitive member to be chemically modified inconveniently. Thus, this kind of photosensitive member is inferior to inorganic photosensitive members such as a-Se and a-Si in durability.
As a measures against the deterioration of the photosensitive member with ozone generated at the time of charging, it has been suggested an electrophotographic photosensitive member having a conductive support, a charge-transporting layer and a charge-generating layer in this order, and an electrophotographic photosensitive member in which a protective layer is disposed on a photosensitive layer, for example, in Japanese Patent Application Laid-open Nos. 61-75355 and 54-58445.
However, in the electrophotographic photosensitive member having such a layer constitution, the relatively thin charge-generating layer is used as an upper layer, and when the member is repeatedly used, the surface of the photosensitive member is severely damaged by abrasion. In the photosensitive member provided with the protective layer for the purpose of solving this problem, this protective layer is an insulating layer, and therefore when the protective layer is repeatedly used, its potential is not stable, so that stable characteristics of the member cannot be maintained.
In view of the foregoing, it is desired to invent an organic electrophotographic photosensitive member which has a conductive support, a charge-generating layer and a charge-transporting layer in this order and which can be used in a condition that a positive pole is charged. However, in order to realize this expectation, a charge-transporting substance having electron-transporting ability is required. Suggested examples of the charge-transporting substance having the electron-transporting ability include 2,4,7-trinitro-9-fluorenone (TNF), dicyanomethylenefluorene carboxylate in Japanese Patent Application Laid-open No. 61-148159, anthraquinodimethane in Japanese Patent Application Laid-open Nos. 63-70257, 63-72664 and 63-104061, 1,4-naphthoquinone in Japanese Patent Application Laid-open No. 63-85749, and diphenyldicyanoethylene in Japanese Patent Application Laid-open Nos. 63-174993. Japanese Patent Application Laid-Open No. Hei 2-97953 suggests an electrophotographic photosensitive member having a charge-generating layer comprising a positive hole-transporting charge-generating material and a small amount of dicyanovinyl compound having a specific constitution.
However, to fill the present demand of a high-quality image, an electrophotographic photosensitive member has been investigated which can sufficiently meet requirements such as sensitivity, potential properties, cost and the compatibility of the charge-transporting substance with an organic solvent or a binder.